Some functions seem to assume that the program paths are formed by a
fully left-associative application of the Seq constructor (as in: Seq
Skip $ Seq Skip $ ... $ Seq Skip Skip). Therefore, this function is
added; it will turn any string of Seq'ed statements into this shape.
Using this function will do no harm (other than possibly spending effort
into doing nothing), so use it accordingly.

And merged it with the edited version we had. It seems that this extra
line is the only thing that changed.

This change allows us to calculate program paths from all programs (as
long as they don't contain any try-catch). Using this, we should be able
to calculate ALL wlps for the programs. However, the checks are not
complete for the whole program, as only program paths up to a certain
length are checked. Any further program paths might say that the program
is (in)correct and give a different result.

The WLP of a subset of statements in the language can now be calculated.
This needs to be extended, but it gives a basic idea of what we can do.

I made new types for the logical expressions (and the mathematical
expression in them) rather than reusing the datatype within the
language. I feel that there's a benefit to separating these, showing
when we're talking about the programs and when we're talking about the
wlp and its calculation and the like. However, this does increase the
amount of types we use. I think the benefit outweighs the cost of having
extra types, but I also feel like we should discuss this :)

Comes with a .cabal file that says to use z3, but you gotta install it
first. This is *kind of* involved and so we should just do that
together.